Combustion in an engine, such as an internal combustion engine, occurs with an amount of fuel and an amount of air present in a cylinder of the engine. The ratio of the amount of air to the amount of fuel is known as the air fuel ratio. Under some conditions, an overly low air fuel ratio may result in increased particulate matter emissions, while an overly high air fuel ratio may result in increased nitrogen oxide (NOx) emissions and higher fuel consumption due to increased pumping losses.
In some approaches, the air fuel ratio may be adjusted by controlling a wastegate on a turbocharger or controlling a variable geometry turbocharger. In this manner, an amount of boost provided by the turbocharger may be adjusted, thereby changing an amount of air available for combustion in the cylinder. By adjusting the boost, however, the engine power output may be affected, even when there is no command to change the engine power. As such, while air fuel ratio control may be improved, overall engine output control may degrade.